Since the first polymer-based electronic memory device was reported by Sliva et al., in 1970, these devices have attracted significant attention. Polymer-based electronic memory has been developed for various applications, including to establish next generation memory devices. Conventional memory devices based on semiconductor integrated circuits play an important role in the development of information technology. Compared with these inorganic memory devices, polymer-based memory devices have several advantages: high structural flexibility, low cost, solution processability, three-dimensional stacking ability, ease of miniaturization, and the ability to tailor properties through molecular design. Resistive-type memory devices store information based on two bistable states, high current (ON) and low current (OFF), depending on the applied voltage. The electrical behaviors of resistive-type memory devices have been explained by several mechanisms, including charge transfer (CT), conformational change, filamentary structures, and charge trapping/detrapping. Furthermore, some studies have reported that materials containing donor–acceptor (D–A) moieties have good charge transfer and bistable electric properties, which are important for enhancing charge transfer. Polyimides (PIs) are well known to be classic high-performance polymers and were first introduced into memory devices by Kang et al., in 2006. These devices exhibit dynamic random access memory (DRAM) behavior. Furthermore, soluble and air-stable organic semiconductors, such as porphyrin-based semiconductors, have received attention because of their ease of processing and ability to be fabricated on a large scale. Porphyrins and porphyrin complexes are field-responsive materials that can be considered as building blocks for synthesizing charge-transporting layers because of their large size, thermal stability, and diversity of coordination and catalytic chemistry. However, very few porphyrin-containing PIs have been explored for use in applications, especially in memory devices. In this work, we designed a novel donor–acceptor system with a functional porphyrin-containing PI, ZnPor-t-DSDA, for resistive-type memory applications (Fig. 1). When ZnPor-t-DSDA was used as a memory material, it exhibited symmetric biswitching and volatile DRAM characteristics in devices using different metals (e.g., Au and Al) as anodes. The coplanar structure that resulted in the short retention time of the DRAM property was also explored by in situ UV-vis absorption spectroscopy. The reason for the symmetric switching behavior is unclear and is under investigation.
Figure 1. The chemical structure of ZnPor-t-DSDA and a schematic diagram of the resistive memory device.
Figure 2. Current–voltage (I–V) characteristics of ITO/ZnPor-t-DSDA (50 ± 3 nm)/Al memory device; Softening and decomposition temperatures measured by TMA and TGA; the appearance of ZnPor-t-DSDA film.
Reference
Ming-Chi Tsai, Chin-Li Wang, Ching-Yao Lin, Chia-Liang Tsai, Hung-Ju Yen, Huei-Chi You and Guey-Sheng Liou, (2016). A novel porphyrin-containing polyimide for memory devices. Polymer Chemistry, 7, 2780-2784. DOI: 10.1039/C6PY00158K
Professor Guey-Sheng Liou
Institute of Polymer Science and Engineering
gsliou@ntu.edu.tw